1. Field of the Invention
The present invention relates to a pipe coupling having a socket capable of being attached to and detached from a mating plug, and more particularly, to a pipe coupling adapted to connect pipe lines for pressurized fluids.
2. Description of the Related Art
There has conventionally been developed a pipe coupling that is provided with a locking mechanism for locking a socket connected to a mating plug. Usually, the socket of the pipe coupling of this type has a series of tapered holes that are arranged at circumferential spaces near its plug inlet. A plurality of locking balls are stored in the tapered holes. Further, the socket is provided with an operating ring, which is slidable between a locked position in which the locking balls are urged radially inward and an unlocked position in which the balls can move radially outward. The operating ring is urged toward the locked position by means of a spring. On the other hand, the body of the mating plug has a locking groove that receives the locking balls.
When one end of the plug is in the plug inlet of the socket, the operating ring of the socket restrains the locking balls from moving centrifugally, thereby keeping the balls in engagement with the locking groove of the plug. Thereupon, the socket and the plug are locked lest they separate from each other. In separating the socket and the plug from each other, the operating ring of the socket is slid. By doing this, the locking balls of the socket are allowed to move centrifugally from the locking groove of the plug, whereupon the socket and the plug are unlocked. In the case where the socket or the plug is provided with a valve, the valve can be opened or closed automatically as the socket and the plug are connected to or separated from each other.
In operation, the pipe coupling constructed in this manner is subjected to a force of pressure from a fluid that flows therethrough and urges the socket and the plug to separate from each other. This force acts as a contact pressure on the respective engaging surfaces of the locking groove of the plug and the locking balls of the socket. If the pressure of the fluid is low, the force never adversely affects the pipe coupling.
If the fluid pressure increases, however, the aforesaid force becomes very high. If the pipe coupling is used in a high-pressure pipe line system in which the fluid pressure is as high as 35 MPa or more, for example, the contact pressure that acts on the locking balls is so high that the pressure-side edge of the locking groove of the plug body undergoes a sag (plastic deformation caused by the high contact pressure on the locking balls). In the worst case, the sag of the locking groove hinders the slide of the operating ring, thereby disabling the socket and the plug from being attached to or detached from each other.
In order to prevent the sag of the locking groove, the contact pressure that acts on each locking ball should be lowered by loading the socket with a large number of balls. To attain this, however, a large number of tapered holes for locking ball retention must be formed in the socket. In consequence, the space between each two adjacent tapered holes is inadequate, thus the strength of the locking ball retaining portion of the socket lowers inevitably. Thus, the number of locking balls can be increased only limitedly.
In consideration of the above, the assignee of the present invention proposed a pipe coupling that can satisfactorily cope with pipe lines in which a pressurized fluid circulates (Jpn. UM Appln. KOKAI Publication No. 7-12693). In this pipe coupling, a socket is provided with first and second rows of locking members (locking balls), while the outer peripheral surface of a plug is formed having first and second locking grooves. The socket and the plug can be locked together in a manner such that the locking members in each row are caused to engage their corresponding locking groove and that the movement of the locking members is restrained by means of an operating ring. With this configuration, the contact pressure that acts on the locking members can be dispersed to prevent the locking grooves of the plug body from sagging. Thus, the socket body and the plug body can be securely attached to and detached from each other.
Since the pipe coupling has a plurality of rows of locking members, it is inevitably long and complicated. In consequence, it cannot be easily reduced in size and weight and entails an increase in cost.
The principal object of the present invention is to provide a small-sized, low-priced pipe coupling, capable of reducing the load that acts on each locking ball even when a compressed fluid circulates therein.
According to the present invention, there is provided a pipe coupling that comprises a socket. The socket has a plurality of locking balls capable of engaging a locking portion on a plug and connected to the plug with the locking balls in engagement with the locking portion of the plug. The socket further includes: a main cylinder having an outer peripheral surface, an inner peripheral surface, and an end portion formed with an inlet capable of receiving the plug; an outer cylinder located close to the end portion of the main cylinder and around the outer peripheral surface thereof with a fixed annular space defined between the outer cylinder and the outer peripheral surface, the end portion of the main cylinder and the inner end portion of the outer cylinder forming a gap having a tapered profile, each of the locking balls being stored in the gap and movable between a position in which the ball projects radially inward from the inner peripheral surface of the main cylinder and a position in which the ball is recessed from the inner peripheral surface; and a thrust cylinder slidably located in the space between the main cylinder and the outer cylinder and urged toward the end portion, the plug being adapted to be prevented from separating from the socket in a manner such that centrifugal movement of the locking balls is prevented by means of the thrust cylinder when the locking balls are situated in the projected position and in engagement with the locking portion of the plug.
According to this pipe coupling, the socket has no holes for holding the locking balls, and the locking balls are stored in the gap existing between the main cylinder and the outer cylinder. Although the locking balls are arranged in a row in the circumferential direction, as in the conventional case, therefore, a pressing load that acts on each locking ball can be lightened considerably, and the resulting pipe coupling can withstand high pressure fluid contained therein (e.g., internal pressure of 500 MPa). Since the locking balls are arranged in a row, moreover, the overall length of the pipe coupling can be made equal to that of a conventional one, and the combining operation for the locking balls is easy.